The present invention relates to a learning control method for controlling a direct fuel injection engine wherein fuel such as gasoline is injected directly into each cylinder to be ignited by a spark plug. Further, the present invention relates to a storage medium storing such a learning control of a direct fuel injection engine.
A direct fuel injection engine wherein fuel such as gasoline is injected directly into each cylinder to be ignited by a spark plug is now put into a practical use. In such a direct fuel injection engine, reduction of the fuel consumption and making higher the output can be attained at the same time through adjustment of the fuel injection timing. In such a direct fuel injection engine, an electromagnetic solenoid is used for injecting fuel into each cylinder since it is necessitated to variably control a fuel injection timing according to an engine load. In order to spray fuel in a fine particle state into a pressurized space inside a cylinder, the electromagnetic solenoid is required to develop a high pressure of tens of atmospheric pressure at an accurate timing.
However, it is difficult to make the electromagnetic solenoid maintain such a high efficiency over a long period of use. To cope with this problem, the repair shops are provided with testing machines for exclusive use for direct fuel injection engines, which are capable of measuring a variation of the fuel injection timing so that the injection timing can be adjusted at regular intervals. However, this means that the direct fuel injection engine cannot maintain its intended efficiency unless it undergoes inspection at the factory provided with the testing machine for exclusive use.
It is accordingly an object of the present invention to provide a method for controlling a direct fuel injection engine, which can solve the above noted problem inherent in the prior art method.
It is a further object of the present invention to provide a control method of the foregoing character which enables a direct fuel injection engine to maintain its intended efficiency over a long period of use.
It is a further object of the present invention to provide a direct fuel injection engine control system for carrying out the control method of the foregoing character.
It is a further object of the present invention to provide a storage medium which stores the control method of the foregoing character.
To accomplish the above objects, the present invention provides a method of controlling a direct fuel injection engine with spark ignition, comprising, under a condition where an ignition timing is constant, varying a fuel injection timing, monitoring a combustion condition of each cylinder before and after the varying of the fuel injection timing, and controlling the fuel injection timing in accordance with a variation of the combustion condition before and after the varying of the fuel injection timing.
Control of the ignition timing is entirely electric and therefore can be accurate. In contrast to this, control of the fuel injection timing is partly mechanical since it is carried out by the use of an electromagnetic solenoid and therefore accurate control of the fuel injection timing is hard to be obtained. According to the present invention, at the time when the detectable ignition timing is constant, the fuel injection timing is not measured but advanced and delayed so as to optimize the combustion condition. Accordingly, even when the electromagnetic solenoid is deteriorated to lower its efficiency and cause a variation of the fuel injection timing, the fuel injection timing can be controlled so as to be optimized, thus making it possible to maintain an intended efficiency of the direct fuel injection engine over a long period of usage.
Particularly, in case ion current is used for detection of a combustion condition, a combustion control apparatus can be obtained at low cost.
The combustion condition can be detected not only by the current value of ion current but various characteristic parameters that are obtained from, for example, a waveform of the current value. The characteristic parameters include various parameters which are determined by an arithmetic processing or the like from an ion current waveform, for example, an integration value of an ion current waveform, a maximum value of a waveform (peak value of waveform) and an average integration value, average maximum value and a moving average of a plurality of ion current waveforms.